The present invention relates to a flow control valve to control the flow of a fluid within a passageway formed within a valve housing. More particularly, the present invention relates to such a flow control valve in which higher flow rates of the fluid is controlled by a primary valve and lower flow rates are controlled by a secondary needle valve positioned to project into an orifice of a secondary passageway formed within the primary valve.
The prior art has provided many different flow control valves to control the flow of a fluid. Typically, flow control valves have a valve to control the flow of the fluid within a passageway of a valve housing. A valve stem connected to the valve moves the valve between an open position, spaced from a valve seat, to allow flow within the passageway and a closed position, seated against a valve seat, to cut off flow within the passageway. As may be appreciated as the valve moves towards the closed position, it becomes increasingly more difficult to precisely control the flow of the fluid because increasingly smaller movements of the valve stem are necessary for such purposes.
Precise flow control, throughout the entire range of valve movement, is necessary in many applications of flow control valves. This is especially true for those processes in which flow requirements are different during start up and steady-state operation. An example of such a process involves cryogenic refrigeration.
In cryogenic refrigeration, cool down of the equipment requires a large flow through a throttling valve. This allows the equipment to be cooled to operating temperature in a reasonable length of time. However, after the operating temperature is reached, a much smaller flow is required that must be precisely controlled. Typically, two valves are employed in parallel for such purposes, a globe valve and a needle valve. The globe valve is used to control flow of the refrigerant for the higher flow rates required during cool down. When normal operating temperature is reached, the globe valve is closed and the needle valve is used for precise control of the lower flow rate of the refrigerant.
As may be appreciated, the provision of two different valves in the same flow circuit is not an attractive solution from the standpoint of cost and complexity. As will be discussed, the present invention provides a single flow control valve that is capable of handling a wide range of flow rates with precise control of lower flow rates occurring near valve closure.
The present invention provides a flow control valve to control fluid flow. In accordance with the present invention, the valve includes a valve housing having a primary passageway for the fluid flow. Flow is controlled within the primary passageway by a primary valve operable for movement between a closed position against a valve seat located within the primary passageway and an open position spaced from the valve seat. This action controls flow rate of the fluid flow between lower flow rates, as the primary valve is moved toward the closed position and higher flow rates, as the primary valve is moved towards the open position. A secondary passageway, formed at least by an orifice, is situated within the primary valve to allow for an ever more increasing passage of the fluid flow through the primary valve as the primary valve is moved towards the closed position. A secondary needle valve projects into the orifice and thereby meters the ever more increasing passage of the fluid flow within the secondary passageway. A valve stem is provided to move the primary valve between the open and closed positions and to regulate the degree to which the secondary needle valve projects into the orifice, thereby to control the ever more increasing passage of the fluid flow and therefore, the fluid flow at the lower flow rates.
The present invention provides a single flow control valve to do away with the need for two different valves and associated flow circuitry to adjust flow at both high and low flow rates. The secondary needle valve allows for precise metering the fluid flow at the low flow rates. As will be discussed, the actuation of the secondary needle valve can be accomplished in by attachment to the valve stem. In such case, the secondary needle valve is moved to effect its metering function. Alternatively, the secondary needle valve can be attached to the valve housing and thus, be fixed in position. Movement of the primary valve alone thereby produces relative movement between the secondary needle valve and the orifice to meter the lower flow rates.
In one aspect of the present invention, the valve housing has a valve stem barrel. A valve guide, located within the valve stem barrel, is provided with a central opening. The valve stem, at one end, projects through the central opening of the valve guide and has an enlarged head. The primary valve is connected to the valve guide such that the primary valve is spaced from the valve guide with the orifice located opposite to the enlarged head of the valve stem. A spring biases the valve guide against the enlarged head of the valve stem so that movement of the valve stem moves the valve guide and the primary valve. The secondary needle valve is connected to the enlarged head of the valve stem so that when the primary valve is in the closed position, movement of the valve stem adjusts the degree to which the secondary needle valve projects into the orifice.
In accordance with such aspect of the present invention, the spring can be set in compression against the valve guide and a spring retainer connected to the valve stem to bias the valve guide against the enlarged head of the valve stem. Movement of the valve stem and therefore, the secondary needle valve when the primary valve is in the closed position, acts against the bias of the spring.
In a further aspect of the present invention, the secondary needle valve can be connected to the valve housing, within the passageway, so as to be located directly opposite to the orifice and so as to be oriented towards the valve seat. As such, movement of the primary valve by the valve stem adjusts the degree to which the secondary needle valve projects into the orifice.
In accordance with this further aspect of the present invention, the valve housing can be provided with a valve stem barrel. The primary passageway can have a throat located opposite to and aligned with the valve stem barrel. In such aspect, the valve seat is of annular configuration and surrounds the throat of the primary passageway. The primary valve has an enlarged portion, connected to one end of the valve steam. The enlarged portion is configured to slide within the valve stem barrel upon movement of the valve stem, thereby to act as a valve guide. A projecting portion of the primary valve, projects from the enlarged portion such that a ring-like seating surface is defined by an undersurface of the enlarged portion to seat against the valve seat when the primary valve is in the closed position. The orifice is located in the projecting portion.
The projecting portion of the primary valve is configured to fit within the throat of the passageway such that as the primary valve is moved to the closed position, the projecting portion enters the throat of the passageway and the fluid predominantly flows through the orifice. The secondary passageway also has at least one internal passage section communicating between the orifice and an outer surface of the enlarged portion of the primary valve.
The at least one internal passage can communicate between the orifice and a lateral surface of the enlarged portion of the primary valve. In a preferred embodiment, the at least one internal passage section can be an axial section extending from the orifice, towards the enlarged portion of the primary valve. A transverse section can communicate between opposite points of the lateral surface of the enlarged portion of the primary valve so as to intersect the axial passageway section.
As an alternative, the at least one internal passage section can communicate between the orifice and the ring-like seating surface such that the secondary passageway is sealed when the primary valve is in the closed position. In such alternative, the at least one internal passageway section can be provided with an axial section extending from the orifice, towards the enlarged portion. At least two lateral sections communicate between the axial channel and the ring-like seating surface.
In any of the foregoing aspects of the present invention involving connection of the secondary needle valve to the valve housing, the connection can be a threaded connection to allow adjustment of the secondary needle valve.